The present invention relates generally to the field of position sensing detectors, and more specifically, to a type of duo-lateral semiconductor based position sensing detector photodiode.
Detection of the position of incident light is crucial to, among other things, systems used for movement monitoring, mirror alignment, optical switches, optical remote control, lens reflection and refraction measurements, distortion and vibration measurements, position and angle sensors, optical range finders, laser displacement sensors, and auto focusing schemes for machine tool alignment and cameras. Various instruments like small discrete detector arrays or multi-element sensors are available for detecting the position of incident light. However, photodiode-based position sensing detectors (PSDs) offer higher position resolution, higher speed response and greater reliability than other solutions. These photodiode based position sensing detectors are made from semiconductors such as silicon materials.
Since silicon has a cut-off wavelength of 1.1 micron, silicon materials are not useful for longer wavelength applications, such as in the 1.3 to 1.55 micron range for communication systems. This range of wavelength is particularly essential for infrared detection, and microscopic spot light detection, among others. Therefore, position sensing detectors employing materials other than silicon, such as indium-gallium-arsenide (InGaAs)/indium-phosphide (InP), which have a cut-off wavelength suitable for photo detection in the 1.3 to 1.55 micron range, have been developed.
Position sensing detectors utilizing InGaAs/InP are available and are classified primarily into two types: one-dimensional and two-dimensional. One-dimensional position sensing detectors are more limited in application than two-dimensional position sensing detectors, since they can only detect movement in one direction. Two-dimensional position sensing detectors are broadly divided into duo-lateral and tetra-lateral types. While, in general, the former suffers primarily from limitations like high dark current, low speed response and complicated application of reverse bias, the latter primarily suffers from low position resolution and lower signal currents.
Therefore there is a need for innovation in the two-dimensional position sensing detectors to improve the aforementioned limitations leading to higher accuracy position sensing.
The present invention improves the resolution and accuracy of the presently known two-dimensional position sensing detectors. Another object of the present invention is to deliver high performance in the 1.3 to 1.55 micron wavelength region.
In a first aspect of the invention, a position sensing detector includes a semi-insulating substrate semiconductor base covered by first and second semiconductor layers. A p-n junction is created between the first and second semiconductor layer. The detector includes a first pair of electrodes electrically coupled to the first semiconductor layer and a second pair of electrodes electrically coupled to a second semiconductor layer.
The second pair of electrodes may be disposed perpendicular to the first pair of electrodes. One of the electrodes of a first pair of electrodes may be a conductor filled trench extending to the first semiconductor layer through the second semiconductor layer. The trench has a passivation layer covering at least part of the trench wall. The first and second pairs of electrodes may further extend substantially to a common plane. The substrate may be InP.
In a second aspect of the invention, a position sensing detector includes a semi-insulating semiconductor substrate, a first semiconductor layer over the substrate, a second semiconductor layer over the first semiconductor layer, and a third semiconductor layer over the second semiconductor layer. The detector further includes a first and second pairs of electrodes disposed perpendicular to each other and a p-n junction between the second and third semiconductor layers.
The third semiconductor layer may be treated to form a p-region to create the p-n junction. The first and second pairs of electrodes may extend substantially to a common plane. The second aspect may have a second semiconductor layer cover part of the first semiconductor layer and be disposed between the first pair of electrodes that are coupled to the first semiconductor layer. Further, the first semiconductor layer may cover part of the substrate. The position sensing detector may also include a conductive extension that is electrically coupled to an electrode and routed to the substrate. The substrate may be InP and the semiconductor layers may be InGaAs or InGaAs/InP.
Operationally, the position sensing detectors are reverse biased. Photovoltaic effect causes generation of p-type and n-type charges, which move toward the p-type and n-type electrodes respectively, thereby causing a current. The currents received at each electrode are measured and point of incidence is determined.